Balanced doublet antenna of small dimension



Dec. 18, 1 956 F. J. LUNDBURG BALANCED DOUBLET ANTENNA OF SMALLDIMENSION Filed Nov. 19

INVENTOR FRANK d. LUNDBURF! ATTORNEY United State atent BALANCED DOUBLETANTENNA OF SMALL DIMENSION Frank J. Lundburg, East Orange, N. J.,assignor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Application November 19, 1949, Serial No.128,332

Claims. (Cl. 343-818) This invention relates to radio antennas and moreparticularly to antennas made of small dimensions.

For convenience of construction and installation it is often desirableto have antennas made of small dimensions. This is particularlydesirable when an antenna of directive characteristics is wanted, as thesmall construction makes physical rotation at relatively high speedpractical. A difficulty arises however in the use of antennas having alength short with respect to a wave length. Such antennas have agenerally low radiation resistance and so are not matched with thetransmission line, thus resulting in inefliciency of operation.

It is an object of my invention to provide a relatively small easilyrotatable antenna, and to use therewith a device for rendering theantenna eificient despite its small dimensions.

According to a feature of my invention I provide an antenna ofrelatively small dimensions, for example, a dipole in the order of fromone to three-tenths overall wave-lengths, and supply about the antenna aloading resonator effectively open about one planar dimension of theantenna to provide a substantial impedance match between the antenna andthe transmission line. The resonator may comprise an open wire cage madeof rods perpendicular to the plane of polarization of the antennacovered at the top and bottom with plane conductive sheets. The antennamay be rotated within the cage resonator construction.

While I have set forth above the objects and features of my inventionthe operation thereof may be best understood from the description of aparticular embodiment thereof made with reference to the accompanyingdrawing, the single figure of which shows an antenna incorporatingfeatures of my invention.

In this figure is shown a dipole antenna 1 supplied with energy over acoupler 2, connected to a feed line 3. Conductive plates 4 and 5 arespaced below and above dipole antenna 1, and these plates areinterconnected by the rods 6, fastened to plates 4 and 5 to providemechanical separation and electrical connection thereto. A rotarymounting may be provided as shown at 7 so that the antenna may berotated independently of the resonator. The length of the dipole antennamay be of any desired length preferably between one twentieth and threetenths wave lengths. The plates and connecting wires form a cavityresonator which serves to raise the impedance of the antenna assembly toproduce an elfective match between the radiating structure and theether. The tie rods are closely enough spaced to form effectively aclosed resonator and a polarizing grating to filter the verticallypolarized components. Horizontally polarized energy, however, readilypasses out around the periphery. While the assembly is completelymatched at only one frequency, it is efiective over a relatively wideband with permissible mismatch.

2,774,967 Patented Dec. 18, 1956 In an actual example of a dipoleradiator of substantially 30 electrical length at 800 megacycles wasprovided. This dipole had a. radiation resistance of three to four. ohmsby itself giving very low efliciency radiation. A resonator cage wasprovided symmetrically about the dipole, the spacing between the platesbeing substantially a half wave length at the operating frequency andthe diameter of the circle being likewise of the same dimensions. Twentyrods spaced uniformly around the periphery were used. With thisarrangement a radiation resistance of approximately 44 ohms wasachieved. This antenna was operated successfully over a wave band ofapproximately 60 megacycles with a mismatch of approximately 2:1.

While the specifiic example described covers a structure which was foundvery good it should be understood that the particular dimensions are notcontrolling.

It is clear that the principles of the invention may be achieved byother structures. The dimensions of the resonator may vary widely, itbeing borne in mind that the essential feature is to provide a loadingresonator for the short dipole to elfect a desired impedancetransformation. Also while any particular structure will have an optimumeffect at the center frequency it is to be understood that the efiectivetolerence of mismatch will permit operation over a relatively widefrequency band with reasonable efliciency. Although the particularexample given is in the range of 800 megacycles it is clear that theinvention may apply to lower frequencies as well, where the normaldimensions are greater so that the reduction in dimensions is of greaterimportance from a standpoint of ready rotatability.

I claim:

1. A radio antenna assembly for radiating a plane polarized wave,comprising a radiating dipole antenna of small length relative to half awave-length at the operating frequency, and a resonator includingconductive vertical supports physically enclosing said antenna but opento radiation in said plane of polarization.

2. A radio antenna according to claim 1, wherein said dipole is betweenone twentieth and three tenths wave length long at the operatingfrequency.

3. A radio antenna assembly comprising a dipole radiator having anoverall length short with respect to a quarter wave length at theoperating frequency, a pair of conductive plates spaced apart onopposite sides of and substantially concentric with a perpendicular axisof said dipole, and a plurality of spaced rods interconnecting saidplates and arranged in a circular pattern, and regularly spaced from oneanother at substantially a tenth wave length, said plates and rodsforming a resonator cage substantially matching the impedance of saidantenna to the radiation space at said operating frequency.

4. A radio antenna assembly comprising a dipole radiator having anoverall length between one twentieth and three tenths wave length at theoperating frequency, a pair of conductive plates spaced apart a halfwave length at the operating frequency on opposite sides of andsubstantially concentric with a perpendicular axis of said dipole, and aplurality of spaced rods interconnecting said plates and arranged in acircular pattern of substantially one half a wave length diameter at theoperating frequency, and spaced from one another substantially a tenthwave length.

5. A radio antenna assembly comprising a radiating antenna of smalllength relative to half a wave length at the operating frequency andcapable of producing directive, substantially plane polarizedradiations, a resonator comprising a pair of plates having conductivesur- 3 t faces spaced on opposite sides of said antenna, and a pluralityof conductive rods perpendicular to the plane of polarization of saiddipole, spaced around the antenna and connected to said plates.

References Cited in the file of this patent UNITED STATES PATENTS 4Katzin Apr. 9, 1946 Hansen Feb. 4, 1947 Montgomery Mar. 25, 1947 AramMar. 29, 1949 Johnson Dec. 5, 1950 Wehner Jan. 30, 1951 Litchford et a1Oct. 23, 1951 FOREIGN PATENTS Australia Dec. 9, 1941

